The present embodiments relate to viscoelasticity measurements. In particular, a viscoelastic property of tissue is measured in vivo.
Shear modulus characteristics of a tissue sample may be measured with a rheometer. A rheometer is a mechanical device capable of subjecting a sample to either a dynamic (e.g., sinusoidal) or static (e.g., linear) deformation. The rheometer may measure the storage shear modulus and the loss shear modulus for a frequency range. The range is limited based on material stiffness, such as 1 to 10 Hz for soft tissue. For medical use, tissue is extracted from a patient for placement in the rheometer. The rheometer is not used for in vivo measurements. The measurements depend on the size and shape of the extracted tissue sample, as well as boundary conditions due to the extraction.
Shear characteristics may be measured in vivo with ultrasound. For example, shear velocity detection is used in various diagnostic applications, such as assessing liver disease. For shear wave detection, an ultrasound pushing pulse (e.g., a one cycle pulse) is fired along a scan line. The pushing pulse generates a shear wave, causing displacement of tissue. The displacement is measured. To detect the shear wave velocity, multiple pushing pulses along a same scan line and corresponding displacement detection scans are used. These shear measurements may have limited information or depend on the compression level.